A rabbit mammary gland receptor assay (RRA) for prolactin will be utilized to determine serum prolactin levels and for structure function studies of prolactin preparations. The RRA will be used to identify and characterize placental lactogens in a number of species in which they have been identified. A RRA for growth hormone (GH) using rabbit liver plasma membranes will be utilized in a search for new growth factors in serum and pituitary extracts. The RRA for GH also will be used in structure function studies of synthetic and chemically modified GH fragments. The receptor for GH and prolactin will be solubilized, purified and characterized. The factors controlling human prolactin secretion in health and disease will be explored. Human prolactin will be isolated from frozen pituitary glands for amino acid sequence analysis. Methods are to be developed for the isolation of human prolactin from amniotic fluid. A human lipolytic peptide, lipotropin has been isolated. A radioimmunoassay for lipotropin will be developed to determine the factors which regulate the secretion of lipotropin. The biological effects of lipotropin are to be examined in vivo and in vitro in animals. A posterior pituitary lobe natriuretic peptide has been isolated from acid extracts of the posterior lobe. The active fraction is to be identified and characterized chemically. Its renal action is to be explored using clearance and micropuncture techniques.